In an image reading apparatus, image copying apparatus, or other paper conveying apparatus, sometimes a jam occurs when paper is conveyed along a conveyance path, multifeed occurs where a plurality of sheets of paper are conveyed along the conveyance path in a superposed state, and other abnormalities may occur when paper is conveyed. In general, a paper conveying apparatus is provided with the function of stopping the operation of the apparatus when a jam or multifeed has occurred.
A jam detection device of a copier which converts a sound which is generated on the conveyance path to an electrical signal and determines that a jam has occurred when the time where the reference level is exceeded exceeds a reference value has been disclosed (see Japanese Laid-Open Patent Publication No. 57-169767).
Further, an ink jet recording apparatus which has a striking means which strikes a recording medium on a conveyance route so as to make it generate a sound and a sound detector which detects the sound which is generated by the striking means is disclosed. This ink jet recording apparatus discriminates the type of recording medium from an electrical signal from the sound detector and sets a recording method or recording pattern in accordance with the recording characteristics of the type of recording medium which is discriminated (see Japanese Laid-Open Patent Publication No. 2003-212386).
Further, a currency or negotiable security or other discriminating apparatus which has a sound generating means for generating a sound during conveyance of currency or a negotiable security etc., and a sound detecting means for detecting the sound which is generated by the sound generating means and which discriminates the genuineness of the currency or negotiable security etc., from the sound which is detected by the sound detecting means is disclosed (see Japanese Laid-Open Patent Publication No. 2000-251108).